Multiple activity rig

ABSTRACT

An offshore platform may include a pair of trolleys. One trolley may be mounted on top of the platform and the other trolley may be suspended below the platform. Each trolley may be positioned on opposed sides of a moon pool in one embodiment of the present invention. The lower trolley may be used to hang off a riser and blowout preventer. The upper trolley may be utilized to hang off smaller diameter casing while larger diameter casing is being made up and positioned within the hole. As a result of the parallel operations made possible by the trolleys, drilling time may be reduced in some embodiments.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based on provisional application No. 60/576,156,filed Jun. 2, 2004.

BACKGROUND

This invention relates generally to offshore drilling of wells usingfloating and non-floating platforms.

A floating platform may be moved to a position over a potential welllocation. The well may be drilled and may be coupled to the rig by amarine riser. Conventionally, there is a substantial distance betweenthe floating platform and the seabed surface. For example, this distancemay be several thousand feet. As a result, it is necessary to lowervarious drill strings, casings, and risers from the surface to theseabed floor.

The cost associated with drilling wells with offshore floating platformsmay be substantial. For example, rental rates for offshore mobileplatforms may run in the range of $300,000.00 a day. Significant timemay be spent running various equipment from the rig down to the subseafloor. This time may result in a substantial portion of the cost.

Often, it is desirable to drill one well, pick up, and move to anotherlocation. The need to connect to a well from the surface involvessubstantial expenditure of time and, therefore, expense.

To address these problems, so-called dual activity rigs have beenproposed. In a dual activity rig there may be two derricks, including amain derrick, used for running and hanging off the blowout preventer,and an auxiliary derrick, used to drill the top hole and run surfacecasing. A blowout preventer riser may be hung off from the rig while thedrill string is operating to form the hole.

Dual operations may save time from the time a rig arrives on location tothe landing of the blowout preventer. This is because the riser and theblowout preventer can be made up and run off line.

Thus, there is a need for still better ways to save time during offshorefloating platform drilling activities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, cross-sectional view of one embodiment of thepresent invention in the course of jetting casing into a seabed;

FIG. 2 is a partial, enlarged, cross-sectional view of a portion of thecasing in position over the seabed floor in accordance with oneembodiment of the present invention;

FIG. 3 is a cross-sectional view of the embodiment shown in FIG. 1 afterthe casing has been jetted into the seabed floor, during drilling of asmaller diameter hole below that casing in accordance with oneembodiment of the present invention;

FIG. 4 is a partial, enlarged, cross-sectional view of the embodimentshown in FIG. 3 in the course of drilling a smaller diameter hole belowa larger diameter casing in accordance with one embodiment of thepresent invention;

FIG. 5 is a cross-sectional view showing the smaller diameter casing inone embodiment;

FIG. 6 is an enlarged, cross-sectional view showing the portion of thewell within the seabed floor, the guide base, and the overlying blowoutpreventer and riser in accordance with one embodiment of the presentinvention;

FIG. 7 is an enlarged, cross-sectional view taken generally along theline 7-7 in FIG. 1 in accordance with one embodiment of the presentinvention; and

FIG. 8 is a partial, enlarged, perspective view of the lower trolley,riser, and blowout preventer hung off of the rig in accordance with oneembodiment of the present invention; and

FIG. 9 is a cross-sectional view of the well with the blowout preventerand riser in position in accordance with one embodiment of the presentinvention.

DETAILED DESCRIPTION

Referring to FIG. 1, a floating platform or multiple operation drillingrig 10 is shown in position over a formation. The rig 10 may include asingle derrick 12, which may include multiple levels for differentoperations. In some embodiments, more than one derrick may be utilized.In the embodiment illustrated, the deck 14 supports an upper trolley 16and a lower trolley 18. The upper trolley 16 may ride on the deck 14 andthe lower trolley 18 may ride on the track beneath the deck 14.

Also beneath the deck 14 are the floats 80. Suspended downwardly is astring 82 coupled to a guide base 35. The guide base 35 is intended tobe positioned on the seabed floor (SB) but, in FIG. 1, is shown beinglowered within the ocean (O). Below the guide base 35 is a largerdiameter casing or conductor 22 in accordance with one embodiment of thepresent invention. The larger diameter casing 22 may be a 36″ casing inone embodiment. The lowermost end of the casing 22 includes a pluralityof high pressure jets capable of displacing the seabed floor and forminga hole that will receive the casing 22.

In the position shown in FIG. 1, the riser 25 and blowout preventer 24are hung off of the lower trolley 18 out of position from the drillstring 82. For example, the rig 10 may have just arrived from a priordrilling site. It may have arrived with the riser 25 and blowoutpreventer 24 hung off of the trolley 18. As a result, there is no needto spend the time making up of the riser 25 and attaching the blowoutpreventer 24 because that equipment is already in position, hung off ofthe rig 10.

Upon arriving at the drilling site, all that would be necessary then isto connect the guide base 35 to the larger diameter casing. In oneembodiment, about 4 joints of 36″ casing may be secured to the guidebase 34 so that the guide base 35 and casing 22 can be lowered on thestring 82 to the seabed floor (SB).

Referring to FIG. 2, once the casing 22 is at the seabed floor, aplurality of high pressure fluid jets 30 may receive pumped fluid andjet that fluid to form a hole H in the seabed floor ahead of a casing22. Thus, as the casing 22 is advanced into the seabed floor, a hole isjetted by an array of three jets 30 in accordance with one embodiment ofthe present invention. This hole is sufficiently large to enable thecasing 22 to be jetted into the seabed floor (SB) and to position theguide base 35 on the seabed floor. Thus, high pressure fluid may bepumped down from the rig 10 and ejected from the jets 30 to removeseabed sediment.

Referring to FIG. 3, after the casing 22 is in place within the seabedfloor (SB) and the guide base 35 is in position on the seabed floor, asmaller diameter bottom hole assembly or drill string 28 may be releasedahead of the casing 22. Then, a smaller diameter hole is drilled usingthe bottom hole assembly 28 as shown in FIG. 3. In effect, the bottomhole assembly 28 simply advances downwardly through the now stationarycasing 22. In one embodiment, the smaller diameter hole may be abouteither 26″ or 17½″ in diameter.

Thus, as shown in FIG. 4, an ever-deeper hole 36 is formed as a resultof the drilling bit (not shown) operating on the end of the bottom holeassembly 28. The depth of the hole 36 that is drilled is limited toprevent the bottom hole assembly 28 from reaching a high pressureformation within the seabed floor. Namely, because no blowout preventeris in place at this time, it is desirable to drill a relatively shallowhole 36 without penetrating any high pressure formations.

The bottom hole assembly 28 is pulled out of the hole 36. Then, thesmaller diameter casing 20 is run into the hole 36, which may just beformed by the bottom hole assembly 28, as shown in FIG. 5. A series ofsections of casing 20 were first pre-assembled and suspended from theupper trolley 16 as shown in FIG. 3. Then, when the bottom hole assembly28 has been removed, the trolley 16 can be rolled into place within thederrick 12 so that the casing 20 may be lowered into the hole 36. Insome embodiments, it may be desirable to add one more joint of casing tothe pre-hung casing before lowering the casing 20 into the hole. Thesmaller diameter casing 20 is moved with the trolley 16 into a main moonpool and then lowered into the hole as shown in FIG. 5.

More particularly, the casing 20 is provided through the guide base 35into the hole 36 to a desired depth. As shown in FIG. 6, the casing 20extends some depth into the seabed floor, passing through the largerdiameter casing 22. The smaller diameter casing 20 may be cemented inposition. Then, the string 84 is pulled out of the hole.

Referring to FIG. 7, the arrangement of the deck 14, in accordance withone embodiment of the present invention, is illustrated. The position ofthe derrick 12 is shown. The moon pool 68 has an extension 62 whichpoints towards the upper trolley 16. The upper trolley 16 includes aslot 90, arranged to mate with the extension 62 on the moon pool 68.

Thus, the trolley 16 may be advanced to the extension 62 where the madeup, hung off, casing 20 has been pre-positioned. The trolley 16 ispositioned so that the slot 90 overlays the extension 62. The tool 72then lifts the casing 20 from the extension 62 and mounts it on thetrolley 16. The trolley 16 thereafter advances over the moon pool 68 sothat the casing 20 may be lowered into the hole 36.

The casing 20 may be stored horizontally on racks 64 and advanced by aconveyor 66. The casing 20 then may be rotated to a vertical orientationand transferred by a crane 69 into the extension 62. A larger crane 70may be utilized to support operations through the moon pool 68.

Referring next to FIG. 8, the lower trolley 18 supports the riser 25 andthe blowout preventer 24, which has already been pre-hung from the lowertrolley 18. The lower trolley 18 may ride on bearings 54, supported by atrack 56 on the deck 14. A split spherical bearing 50 includes portion50 a and 50 b and is openable in the directions indicated by the arrowsB. In other words, the bearing 50 includes two portions 50 a and 50 bwhich support the riser 25 on the ring 52 thereof. When the bearing 50is opened, the riser 25 and blowout preventer 24 may be lifted from thetrolley 18 and moved into the moon pool 68.

Finally, referring to FIG. 9, the riser 25 and blowout preventer 24,once in position under the derrick 12, may be lowered into position andsecured to the guide base 35. After the sequence described herein,conventional completion and production techniques may be used.

Once the well is completed, and it is desired to move to anotherlocation, the operation may be reversed. The blowout preventer 24 andriser 25 may be removed from the guide base 35, reattached to thetrolley 18, and moved to the stored position shown in FIG. 1. Then, therig 10 may be moved to a new location with the blowout preventer 24 andriser 25 hung off from the rig 10.

In some embodiments of the present invention, substantial time may besaved in offshore drilling operations. These savings arise by virtue ofthe fact that multiple operations may be done in a parallel, rather thanserially. For example, the smaller diameter casing 20 is pre-made upand, therefore, the time to make up the casing does not add to theoverall drilling time. That is, the casing 20 was made up while thecasing 22 was being jetted in. Likewise, the cementing and the runningin of the smaller diameter casing 20 may be partly done offline, as maybe the removal of the landing string from the hole. Finally, the time torun in the blowout preventer 24 may be substantially shortened becausethe blowout preventer 24 has already been made up and hung off, offline.

Thus, in some cases, from 2 to 4 days may be saved over other techniqueswhen drilling in water depths on the order of 5000 feet. Of course, thepresent invention is in no way limited to any particular drilling depthand may be applicable to any of a variety of well depths. While afloating embodiment is depicted, fixed or stationary platforms may alsobe used in some cases.

While the present invention has been described with respect to a limitednumber of embodiments, those skilled in the art will appreciate numerousmodifications and variations therefrom. It is intended that the appendedclaims cover all such modifications and variations as fall within thetrue spirit and scope of this present invention.

What is claimed is:
 1. A method comprising: hanging off a first casingfrom a trolley mounted on an offshore drilling platform; positioning asecond casing having a larger diameter than the first casing withoutusing said trolley when said first casing is hanging off from thetrolley; repositioning the first casing by rolling the trolley into aposition over the second casing when the second casing is in positionwithin the seabed floor; jetting in the second casing; and inserting adrill string through the second casing to drill a hole for the firstcasing.
 2. The method of claim 1 including lowering the first casinginto the hole below the second casing.
 3. The method of claim 1including hanging off a blowout preventer and riser from said platform.4. The method of claim 3 including hanging off said blowout preventerand riser from a lower trolley on said platform while hanging off saidfirst casing from said trolley mounted on said platform and positioningsaid second casing.
 5. The method of claim 4 including providing anextension on a moon pool in said platform and providing a matingextension on said trolley mounted on said platform to enable said firstcasing to be lifted from said moon pool extension and positioned oversaid moon pool.
 6. A method comprising: hanging off a first casing froma trolley mounted on an offshore drilling platform; positioning a secondcasing having a larger diameter than the first casing without using saidtrolley when said first casing is hanging off from the trolley;repositioning the first casing by rolling the trolley into a positionover the second casing when the second casing is in position within theseabed floor; hanging off a blowout preventer and riser from saidplatform; and hanging off said blowout preventer and riser from a lowertrolley on said platform while hanging off said first casing from saidtrolley mounted on said platform and positioning said second casing. 7.The method of claim 6 including jetting in the second casing.
 8. Themethod of claim 7 including inserting a drill string through the secondcasing to drill a hole for the first casing.
 9. The method of claim 8including lowering the first casing into the hole below the secondcasing.
 10. The method of claim 9 including providing an extension on amoon pool in said platform and providing a mating extension on saidtrolley mounted on said platform to enable said first casing to belifted from said moon pool extension and positioned over said moon pool.